There is considerable interest in the treatment of wastewater sludge. Anaerobic digestion of municipal wastewater sludge typically requires the use of large holding tanks sized to accommodate enough sludge to account for a 20-day hydraulic retention time. In addition to these tanks, equipment is used to constantly stir the contents. This new process requires a much smaller tank and no stirring equipment, and yet does not sacrifice performance as compared to standard anaerobic digestion processes. Resulting equipment costs and capital costs are reduced considerably. Land requirements are similarly reduced.
Anaerobic digestion is a microbiological process in which organic materials are broken down by the action of microorganisms in the absence of oxygen. The anaerobic microorganisms reduce the quantity of organic matter present in the biologically activated sludge thereby generating bio-gas having a relatively high methane gas content. The stabilized sludge is typically removed from a digestion tank for dewatering and disposal. The methane gas can be burned off or recovered to supply energy to heat the digesters as well as supply energy for use elsewhere in the treatment facility. There exists a great need to maximize the effectiveness and costs of the anaerobic digestion to allow municipalities and other treatment facilities to operate efficiently and reduce the burdens on space. This invention serves these important needs and others as will become apparent.